Abstract Attention Deficit Hyperactivity Disorder (ADHD) is a common childhood disorder and is associated with wide- ranging impairments and negative health outcomes, including those that persist into adulthood and have significant public health consequences. Children with ADHD are at increased risk for not achieving recommended amounts of physical activity (PA) and engaging in high rates of sedentary behaviors like media use. PA is found to improve cognitive functioning and decrease ADHD symptoms, but is usually not addressed in standard treatment for ADHD. In this two-phase R21/R33 application, we propose to develop and pilot an intervention to increase PA and healthy behaviors in children with ADHD using a family-focused treatment model. In the R21 phase (n=30), we will pilot a group parent intervention based on the front-line behavioral treatment for ADHD, parent Behavior Management Training (BMT), adapted to focus on increasing PA and integrated with mobile Health technology (i.e., wearable PA trackers) and social media (Facebook) support to increase engagement and longevity of effects. We will evaluate feasibility, acceptability, and effects of the intervention to increase PA. In the R33 phase (n=80), we will conduct a small randomized trial comparing the novel PA-focused intervention with standard BMT and examine effects on PA, other health behaviors, ADHD symptoms and functioning, and family outcomes across a 1-year period. Findings will inform a future large- scale evaluation of intervention effects on long-term health and functioning for children with ADHD.